The seventh book, the Uttara Kanda, which contains the banishment and the swallowing by the earth, is regarded by most scholars as a later addition to Valmiki's epic, along with the first book. That is a text-critical judgement, not a devotional one, and it is not a way of making the problem go away: the fire ordeal is in the sixth book, in the older layer.
The retellings handle the ending very differently. Tulsidas, in the sixteenth-century Awadhi version most of north India knows, uses a device that removes the ordeal's sting: the Sita abducted by Ravana is a shadow or illusory Sita, the real one having been hidden in fire beforehand, so the fire ordeal returns the true Sita rather than testing her. Some regional versions omit the banishment entirely. Others, particularly in Telugu, Tamil and Bengali women's oral traditions, expand her side of it, songs sung by women at weddings and while working that give Sita complaints, anger, and a voice the Sanskrit does not.
That body of women's oral Ramayana material is substantial and has been collected and studied since the mid twentieth century. It is a corrective to the assumption that the tradition speaks with one voice about her, and it long predates the modern feminist readings that reached the same conclusions from outside.
The Jain versions restructure the story more drastically still. In several, Sita becomes a Jain nun at the end, which resolves the difficulty by taking her out of the marriage rather than out of the world.